U.S. patent application number 12/509963 was filed with the patent office on 2010-05-06 for superconductor cooling system and superconductor cooling method.
This patent application is currently assigned to MITSUBISHI HEAVY INDUSTRIES, LTD.. Invention is credited to Hiroshi KAWASHIMA.
Application Number | 20100113282 12/509963 |
Document ID | / |
Family ID | 42132151 |
Filed Date | 2010-05-06 |
United States Patent
Application |
20100113282 |
Kind Code |
A1 |
KAWASHIMA; Hiroshi |
May 6, 2010 |
SUPERCONDUCTOR COOLING SYSTEM AND SUPERCONDUCTOR COOLING METHOD
Abstract
A superconductor cooling system has: a first superconductor; a
first cooling conductor used for cooling the first superconductor;
a first cooling unit configured to cool the first cooling conductor
to a first temperature; and a current lead configured to supply a
current to the first superconductor. Here, a part of a path of the
current is formed of a second superconductor. The superconductor
cooling system further has: a second cooling conductor used for
cooling the second superconductor; a second cooling unit configured
to cool the second cooling conductor to a second temperature; and a
first thermal conduction switch connected between the first cooling
conductor and the second cooling conductor to ON and OFF heat
transfer between the first cooling conductor and the second cooling
conductor.
Inventors: |
KAWASHIMA; Hiroshi; (Hyogo,
JP) |
Correspondence
Address: |
KANESAKA BERNER AND PARTNERS LLP
1700 DIAGONAL RD, SUITE 310
ALEXANDRIA
VA
22314-2848
US
|
Assignee: |
MITSUBISHI HEAVY INDUSTRIES,
LTD.
Tokyo
JP
|
Family ID: |
42132151 |
Appl. No.: |
12/509963 |
Filed: |
July 27, 2009 |
Current U.S.
Class: |
505/163 ;
165/277 |
Current CPC
Class: |
H01F 6/04 20130101; F25D
19/006 20130101; F25B 9/10 20130101 |
Class at
Publication: |
505/163 ;
165/277 |
International
Class: |
H01L 39/02 20060101
H01L039/02; F28F 27/00 20060101 F28F027/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 30, 2008 |
JP |
2008-280366 |
Claims
1. A superconductor cooling system comprising: a first
superconductor; a first cooling conductor used for cooling said
first superconductor; a first cooling unit configured to cool said
first cooling conductor to a first temperature; a current lead
configured to supply a current to said first superconductor,
wherein a part of a path of said current is formed of a second
superconductor; a second cooling conductor used for cooling said
second superconductor; a second cooling unit configured to cool
said second cooling conductor to a second temperature; and a first
thermal conduction switch connected between said first cooling
conductor and said second cooling conductor to ON and OFF heat
transfer between said first cooling conductor and said second
cooling conductor.
2. The superconductor cooling system according to claim 1, wherein
said first thermal conduction switch is turned ON in an initial
cooling period before said current is supplied to said first
superconductor, and wherein said first thermal conduction switch is
turned OFF after said initial cooling period.
3. The superconductor cooling system according to claim 2, further
comprising: a first temperature sensor configured to detect a
temperature of said first cooling conductor, wherein when said
temperature of said first cooling conductor becomes equal to or
lower than a predetermined temperature, said first temperature
sensor deactivates a first switch signal, and said first thermal
conduction switch is turned OFF in response to the deactivation of
said first switch signal.
4. The superconductor cooling system according to claim 2, further
comprising: a second temperature sensor configured to detect a
temperature of said second cooling conductor, wherein when said
temperature of said second cooling conductor becomes equal to or
lower than a predetermined temperature, said second temperature
sensor deactivates a second switch signal, and said first thermal
conduction switch is turned OFF in response to the deactivation of
said second switch signal.
5. The superconductor cooling system according to claim 2, wherein
said first thermal conduction switch is turned ON in a heating
period after the supply of said current to said first
superconductor is ended.
6. The superconductor cooling system according to claim 1, wherein
said second cooling conductor comprises: a current lead connector
located on a side of said second superconductor; a cooling unit
connector located on a side of said second cooling unit; and a
second thermal conduction switch connected between said current
lead connector and said cooling unit connector to ON and OFF heat
transfer between said current lead connector and said cooling unit
connector, wherein said first thermal conduction switch is
connected between said first cooling conductor and said cooling
unit connector to ON and OFF heat transfer between said first
cooling conductor and said cooling unit connector.
7. The superconductor cooling system according to claim 6, wherein
said first thermal conduction switch is turned ON and said second
thermal conduction switch is turned OFF in an initial cooling
period before said current is supplied to said first
superconductor, and wherein said first thermal conduction switch is
turned OFF and said second thermal conduction switch is turned ON
after said initial cooling period.
8. The superconductor cooling system according to claim 7, further
comprising: a first temperature sensor configured to detect a
temperature of said first cooling conductor, wherein when said
temperature of said first cooling conductor becomes equal to or
lower than a predetermined temperature, said first temperature
sensor deactivates a first switch signal, and said first thermal
conduction switch is turned OFF in response to the deactivation of
said first switch signal.
9. The superconductor cooling system according to claim 8, further
comprising: a second temperature sensor configured to detect a
temperature of said cooling unit connector, wherein when said
temperature of said cooling unit connector becomes equal to or
lower than a predetermined temperature, said second temperature
sensor activates a second switch signal, and said second thermal
conduction switch is turned ON in response to the activation of
said second switch signal.
10. The superconductor cooling system according to claim 7, further
comprising: a second temperature sensor configured to detect a
temperature of said cooling unit connector, wherein when said
temperature of said cooling unit connector becomes equal to or
lower than a predetermined temperature, said second temperature
sensor activates a second switch signal, said first thermal
conduction switch is turned OFF in response to the activation of
said second switch signal, and said second thermal conduction
switch is turned ON in response to the activation of said second
switch signal.
11. The superconductor cooling system according to claim 7, wherein
said first thermal conduction switch and said second thermal
conduction switch are turned ON in a heating period after the
supply of said current to said first superconductor is ended.
12. The superconductor cooling system according to claim 1, wherein
said first temperature is lower than said second temperature.
13. A superconductor cooling method in a superconductor cooling
system, wherein said superconductor cooling system comprises: a
first superconductor; a first cooling conductor used for cooling
said first superconductor; a first cooling unit configured to cool
said first cooling conductor to a first temperature; a current lead
configured to supply a current to said first superconductor,
wherein a part of a path of said current is formed of a second
superconductor; a second cooling conductor used for cooling said
second superconductor; and a second cooling unit configured to cool
said second cooling conductor to a second temperature, wherein said
superconductor cooling method comprises: performing an initial
cooling by connecting between said first cooling conductor and said
second cooling conductor to cool said first superconductor, before
said current is supplied to said first superconductor; and
performing a late cooling after said initial cooling, by
disconnecting said first cooling conductor and said second cooling
conductor from each other to cool said first superconductor and
said second superconductor to said first temperature and said
second temperature, respectively.
14. The superconductor cooling method according to claim 13,
wherein said second cooling conductor includes: a current lead
connector located on a side of said second superconductor; and a
cooling unit connector located on a side of said second cooling
unit, wherein said performing said initial cooling comprises:
connecting between said first cooling conductor and said cooling
unit connector; and disconnecting said current lead connector and
said cooling unit connector from each other, wherein said
performing said late cooling comprises: disconnecting said first
cooling conductor and said cooling unit connector from each other;
and connecting between said current lead connector and said cooling
unit connector.
15. The superconductor cooling method according to claim 13,
wherein said first temperature is lower than said second
temperature.
Description
INCORPORATION BY REFERENCE
[0001] This application is based upon and claims the benefit of
priority from Japanese patent application No. 2008-280366, filed on
Oct. 30, 2008, the disclosure of which is incorporated herein in
its entirety by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a system and a method for
cooling superconductors.
[0004] 2. Description of Related Art
[0005] A superconducting electromagnet device using a
superconducting coil put in a vacuum insulation container is known
(refer to Japanese Laid-Open Patent Application JP-H07-142237 and
Japanese Laid-Open Patent Application JP-2004-111581, for example).
Such a superconducting coil is cooled by a superconducting coil
cooling unit and goes into a superconducting state under an
extremely-low temperature condition. It is possible to generate a
strong magnetic field by supplying a current to the superconducting
coil in the superconducting state. Here, a member for externally
supplying the current to the superconducting coil is generally
called a "current lead". That is to say, a drive current is
supplied to the superconducting coil through the current lead when
driving the superconducting coil.
[0006] In such a superconducting electromagnet device, heat
intrusion caused by Joule heating at the current lead due to the
current at the time of power distribution and heat intrusion from
the outside of the vacuum insulation container to the
superconducting coil through the current lead occur. In order to
reduce the heat intrusion, a part of a current path in the current
lead may be formed of a superconductor (refer to Japanese Laid-Open
Patent Application JP-H07-142237 and Japanese Laid-Open Patent
Application JP-2004-111581). Under the extremely-low temperature
condition, an electric resistance of the superconductor in the
current lead becomes small while heat resistance thereof becomes
large. In this case, however, it is necessary to provide a current
lead cooling unit for cooling the superconductor in the current
lead, in addition to the superconducting coil cooling unit for
cooling the superconducting coil. The superconductor in the current
lead can be cooled without increasing heat load on the
superconducting coil cooling unit.
[0007] To cool the superconducting coil rapidly to a target
temperature means reduction in a time to starting-up of an
operation of the superconducting coil. It is therefore important to
reduce a cooling time of the superconducting coil. However, to
unnecessarily increase cooling capacity of the superconducting coil
cooling unit or to provide an additional superconducting coil
cooling unit is not preferable, because it causes increase in costs
and may be physically difficult in terms of a placement space.
SUMMARY
[0008] An object of the present invention is to provide a technique
that can reduce a cooling time of a first superconductor in a case
where a part of a current lead for supplying a current to the first
superconductor is formed of a second superconductor.
[0009] In an aspect of the present invention, a superconductor
cooling system is provided. The superconductor cooling system has:
a first superconductor; a first cooling conductor used for cooling
the first superconductor; a first cooling unit configured to cool
the first cooling conductor to a first temperature; and a current
lead configured to supply a current to the first superconductor. In
the current lead, a part of a path of the current is formed of a
second superconductor. The superconductor cooling system further
has: a second cooling conductor used for cooling the second
superconductor; a second cooling unit configured to cool the second
cooling conductor to a second temperature; and a first thermal
conduction switch connected between the first cooling conductor and
the second cooling conductor to ON and OFF heat transfer between
the first cooling conductor and the second cooling conductor.
[0010] In another aspect of the present invention, a superconductor
cooling method in a superconductor cooling system is provided. The
superconductor cooling system has: a first superconductor; a first
cooling conductor used for cooling the first superconductor; a
first cooling unit configured to cool the first cooling conductor
to a first temperature; and a current lead configured to supply a
current to the first superconductor. In the current lead, a part of
a path of the current is formed of a second superconductor. The
superconductor cooling system further has: a second cooling
conductor used for cooling the second superconductor; and a second
cooling unit configured to cool the second cooling conductor to a
second temperature. The superconductor cooling method includes:
performing an initial cooling by connecting between the first
cooling conductor and the second cooling conductor to cool the
first superconductor, before the current is supplied to the first
superconductor; and performing a late cooling after the initial
cooling, by disconnecting the first cooling conductor and the
second cooling conductor from each other to cool the first
superconductor and the second superconductor to the first
temperature and the second temperature, respectively.
[0011] According to the present invention, the cooling time of the
first superconductor can be reduced in the case where a part of the
current lead for supplying the current to the first superconductor
is formed of the second superconductor.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a schematic view showing a configuration of a
superconductor cooling system according to a first embodiment of
the present invention;
[0013] FIG. 2 shows one example of a thermal conduction switch;
[0014] FIG. 3 is a schematic view showing an operation at a time of
initial cooling according to the first embodiment;
[0015] FIG. 4 is a schematic view showing an operation at a time of
late cooling and running according to the first embodiment;
[0016] FIG. 5 is a schematic view showing an operation at a time of
heating according to the first embodiment;
[0017] FIG. 6 is a schematic view showing a configuration of a
superconductor cooling system according to a second embodiment of
the present invention;
[0018] FIG. 7 is a schematic view showing an operation at a time of
initial cooling according to the second embodiment;
[0019] FIG. 8 is a schematic view showing an operation at a time of
late cooling and running according to the second embodiment;
and
[0020] FIG. 9 is a schematic view showing an operation at a time of
heating according to the second embodiment.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0021] The invention will be now described herein with reference to
illustrative embodiments. Those skilled in the art will recognize
that many alternative embodiments can be accomplished using the
teachings of the present invention and that the invention is not
limited to the embodiments illustrated for explanatory
purposed.
1. First Embodiment
1-1. Configuration
[0022] FIG. 1 is a schematic view showing a configuration of a
superconductor cooling system 1 according to a first embodiment of
the present invention. The superconductor cooling system 1 has a
vacuum insulation container 2 in which an internal superconductor
10 is placed. The outside of the vacuum insulation container 2 is a
normal temperature region (NT). On the other hand, the inside of
the vacuum insulation container 2 where the internal superconductor
10 is placed is an extremely-low temperature region (ELT).
[0023] The internal superconductor 10 (first superconductor), which
is used for a superconducting coil for example, goes into a
superconducting state under an extremely-low temperature condition.
It is possible to generate a strong magnetic field by supplying a
current to the internal superconductor 10 in the superconducting
state. A target temperature (first temperature) of the internal
superconductor 10 at this time is 20 K for example.
[0024] A first cooling unit 100 is a cooling device (refrigerator)
used for cooling the internal superconductor 10. More in detail, a
first cooling conductor 110 used for cooling the internal
superconductor 10 is provided within the vacuum insulation
container 2. The first cooling conductor 110 is a copper conductor,
for example. The first cooling unit 100 is connected to the first
cooling conductor 110 and configured to cool the first cooling
conductor 110 down to the above-mentioned first temperature.
Additionally, a first temperature sensor 120 for detecting a
temperature T1 of the first cooling conductor 110 may be provided
within the vacuum insulation container 2.
[0025] A current lead 30 is a member for supplying a current to the
internal superconductor 10 and is connected between an external
power supply 60 outside the vacuum insulation container 2 and the
internal superconductor 10 inside the vacuum insulation container
2. Here, heat intrusion caused by Joule heating at a
normal-conducting current lead 30-1 at the time of power
distribution and heat intrusion from the normal temperature region
NT to the internal superconductor 10 through the current lead 30
may occur. In order to reduce the heat intrusion, a part of the
current path in the current lead 30 is formed of a superconductor
20 (second superconductor). Under the extremely-low temperature
condition, an electric resistance of the superconductor 20 becomes
small while heat resistance thereof becomes large, which is
preferable.
[0026] More specifically, as shown in FIG. 1, the current lead 30
includes a normal-conducting current lead 30-1 provided on a side
of the external power supply 60 and a superconducting current lead
30-2 provided on a side of the internal superconductor 10. The
normal-conducting current lead 30-1, which is a current lead using
ordinary metallic material, is connected to the external power
supply 60 through an electrical conductor 40. On the other hand,
the superconducting current lead 30-2 is a current lead using the
superconductor 20. The superconductor 20 is connected to the
internal superconductor 10 through an electrical conductor 50. At a
time of driving the internal superconductor 10, the current is
supplied from the external power supply 60 to the internal
superconductor 10 through the normal-conducting current lead 30-1
and the superconducting current lead 30-2. A target temperature
(second temperature) of the superconductor 20 at this time is 60 K
for example.
[0027] A second cooling unit 200 is a cooling device (refrigerator)
used for cooling the superconductor 20 of the current lead 30. More
in detail, a second cooling conductor 210 used for cooling the
superconductor 20 is provided within the vacuum insulation
container 2. The second cooling conductor 210 is a copper
conductor, for example. The second cooling unit 200 is connected to
the second cooling conductor 210 and is configured to cool the
second cooling conductor 210 down to the above-mentioned second
temperature. Additionally, a second temperature sensor 220 for
detecting a temperature T2 of the second cooling conductor 210 may
be provided within the vacuum insulation container 2.
[0028] In the present embodiment, the first temperature (e.g. 20 K)
as the target temperature of the internal superconductor 10 is
lower than the second temperature (e.g. 60 K) as the target
temperature of the superconductor 20. The reason is as follows.
First, the second temperature is set to near the upper limit of a
usage temperature of the superconductor 20, from a viewpoint of
optimization of current and heat conductive characteristics of the
superconductor 20, an efficiency of the second cooling unit 200,
reduction in an operating cost and so on. On the other hand, the
first temperature is set far lower than the second temperature in
order to use the internal superconductor 10 with higher performance
and stably use the internal superconductor 10.
[0029] A heater 300 is provided in order to effectively perform a
heating operation when the vacuum insulation container 2 is open.
For example, the heater 300 is connected to the second cooling
conductor 210.
[0030] As shown in FIG. 1, the superconductor cooling system 1 of
the present embodiment is further provided with a first thermal
conduction switch SW1 connected between the first cooling conductor
110 and the second cooling conductor 210. The first thermal
conduction switch SW1 turns ON/OFF heat transfer between the first
cooling conductor 110 and the second cooling conductor 210.
[0031] FIG. 2 shows one example of the first thermal conduction
switch SW1. The first thermal conduction switch SW1 has a
connecting conductor 80 which can physically connect the first
cooling conductor 110 and the second cooling conductor 210.
Preferably, the connecting conductor 80 is made of the same
material (e.g. copper) as the first cooling conductor 110 and the
second cooling conductor 210. The connecting conductor 80 is
connected to an operating portion 82 through a thermal insulator
81. By moving the operating portion 82, the connecting conductor 80
can be brought into contact with the first cooling conductor 110
and the second cooling conductor 210 and can be detached from the
first cooling conductor 110 and the second cooling conductor 210.
That is to say, ON/OFF control of the first thermal conduction
switch SW1 is possible.
[0032] When the first thermal conduction switch SW1 is turned ON,
the connecting conductor 80 is in contact with the first cooling
conductor 110 and the second cooling conductor 210. As a result,
the first cooling conductor 110 and the second cooling conductor
210 are physically connected through the connecting conductor 80
and thus the heat transfer is possible between the first cooling
conductor 110 and the second cooling conductor 210. On the other
hand, when the first thermal conduction switch SW1 is turned OFF,
the connecting conductor 80 is detached from the first cooling
conductor 110 and the second cooling conductor 210. As a result,
the first cooling conductor 110 and the second cooling conductor
210 are disconnected from each other and thus the heat transfer
between the first cooling conductor 110 and the second cooling
conductor 210 is prevented.
[0033] Turning ON/OFF of the first thermal conduction switch SW1
may be performed manually or may be controlled automatically. In
the case of the automatic control, the operating portion 82 is
connected to an actuator. The actuator operates to ON/OFF control
of the first thermal conduction switch SW1, depending on the
temperature T1 of the first cooling conductor 110 detected by the
first temperature sensor 120 or the temperature T2 of the second
cooling conductor 210 detected by the second temperature sensor
220.
[0034] Alternatively, the first thermal conduction switch SW1 may
be formed of bimetal whose shape and displacement are changed
depending on temperature. For example, the bimetal is so formed as
to be in contact with one of the first cooling conductor 110 and
the second cooling conductor 210. When the temperature of the
bimetal is higher than a predetermined temperature, the bimetal
also comes into contact with the other of the first cooling
conductor 110 and the second cooling conductor 210 as well.
Consequently, the first thermal conduction switch SW1 is turned to
the ON state. On the other hand, when the temperature of the
bimetal is equal to or lower than the predetermined temperature,
the bimetal is detached from the other of the first cooling
conductor 110 and the second cooling conductor 210. Consequently,
the first thermal conduction switch SW1 is turned to the OFF
state.
1-2. Operation
[0035] Next, operations of the superconductor cooling system 1
according to the present embodiment will be described below. The
operations of the superconductor cooling system 1 are roughly
divided into: (1) a "cooling stage" for cooling the internal
superconductor 10 and the superconductor 20 to near the respective
target temperatures, before the power distribution to the internal
superconductor 10; (2) a "running stage" for maintaining respective
temperatures of the internal superconductor 10 and the
superconductor 20, during the power distribution to the internal
superconductor 10; and (3) a "heating stage" for heating the
internal superconductor 10 and the superconductor 20, after the
power distribution to the internal superconductor 10 is ended.
Furthermore, according to the present embodiment, the
above-mentioned cooling stage is further divided into an "initial
cooling stage" and a "late cooling stage" performed after the
initial cooling stage. In the following description, the target
temperature (first temperature) of the internal superconductor 10
is 20 K and the target temperature (second temperature) of the
superconductor 20 is 60 K.
[Initial Cooling Stage]
[0036] FIG. 3 is a schematic view showing an operation at the time
of initial cooling. At the time of the initial cooling, the first
cooling unit 100 and the second cooling unit 200 are turned ON and
the heater 300 is turned OFF. Further, according to the present
embodiment, the first thermal conduction switch SW1 is turned ON.
Consequently, the first cooling conductor 110 and the second
cooling conductor 210 are connected with each other and thus the
heat transfer between the first cooling conductor 110 and the
second cooling conductor 210 is possible. As a result, the internal
superconductor 10 is cooled (heat removal) through both of the
first cooling conductor 110 and the second cooling conductor 210.
That is to say, not only the first cooling unit 100 but also the
second cooling unit 200, which is originally used for cooling the
superconductor 20, is used together during the initial cooling of
the internal superconductor 10. Since the first cooling unit 100
whose lowest reachable temperature is low but whose cooling
capacity is small and the second cooling unit 200 whose lowest
reachable temperature is high but whose cooling capacity is large
are used together, a total cooling capacity is improved and thus
the initial cooling can be performed in a short time.
[0037] The first thermal conduction switch SW1 may be turned ON
manually by an operator.
[0038] Alternatively, the first thermal conduction switch SW1 may
be turned ON automatically. For example, the first temperature
sensor 120 detects the temperature T1 of the first cooling
conductor 110 and outputs a first switch signal S1 depending on the
detected temperature T1. The second temperature sensor 220 detects
the temperature T2 of the second cooling conductor 210 and outputs
a second switch signal S2 depending on the detected temperature T2.
The first thermal conduction switch SW1 is turned ON and OFF in
response to the first switch signal S1 or the second switch signal
S2. For example, when the temperature T1 of the first cooling
conductor 110 is higher than a predetermined temperature (e.g. 60
K), the first temperature sensor 120 activates the first switch
signal S1. When the first switch signal S1 is activated, the first
thermal conduction switch SW1 is turned ON. Alternatively, when the
temperature T2 of the second cooling conductor 210 is higher than a
predetermined temperature (e.g. 90 K), the second temperature
sensor 220 activates the second switch signal S2. When the second
switch signal S2 is activated, the first thermal conduction switch
SW1 is turned ON.
[0039] Alternatively, the first thermal conduction switch SW1 may
be formed of bimetal. For example, the bimetal is so formed as to
be in contact with the first cooling conductor 110. When the
temperature T1 of the first cooling conductor 110 is higher than a
predetermined temperature (e.g. 60 K), the bimetal also comes into
contact with the second cooling conductor 210 as well.
Consequently, the first thermal conduction switch SW1 is turned ON.
Alternatively, the bimetal is so formed as to be in contact with
the second cooling conductor 210. When the temperature T2 of the
second cooling conductor 210 is higher than a predetermined
temperature (e.g. 90 K), the bimetal also comes into contact with
the first cooling conductor 110 as well. Consequently, the first
thermal conduction switch SW1 is turned ON.
[Late Cooling Stage and Running Stage]
[0040] FIG. 4 is a schematic view showing an operation at the time
of late cooling and running. As shown in FIG. 4, the first thermal
conduction switch SW1 is turned OFF. Consequently, the first
cooling conductor 110 and the second cooling conductor 210 are
disconnected from each other and thus the heat transfer between the
first cooling conductor 110 and the second cooling conductor 210 is
prevented. At this time, the internal superconductor 10 is cooled
(heat removal) by the first cooling unit 100 through the first
cooling conductor 110. Also, the superconductor 20 is cooled (heat
removal) by the second cooling unit 200 through the second cooling
conductor 210.
[0041] When the first cooling conductor 110 and the internal
superconductor 10 are cooled to near the first temperature (20 K)
and the second cooling conductor 210 and the superconductor 20 are
cooled to near the second temperature (60 K), the late cooling is
ended. After that, the current is supplied to the internal
superconductor 10 from the external power supply 60 through the
current lead 30. At the time of the power distribution to the
internal superconductor 10 (the running stage), the first thermal
conduction switch SW1 is maintained at the OFF state. The
temperature of the internal superconductor 10 is maintained by the
first cooling unit 100, and the temperature of the superconductor
20 is maintained by the second cooling unit 200.
[0042] The first thermal conduction switch SW1 may be turned OFF
manually by an operator.
[0043] Alternatively, the first thermal conduction switch SW1 may
be turned OFF automatically. For example, when the temperature T1
of the first cooling conductor 110 becomes equal to or lower than a
predetermined temperature (e.g. 60 K, which is the target
temperature of the superconductor 20), the first temperature sensor
120 deactivates the first switch signal S1. Then, the first thermal
conduction switch SW1 is turned OFF in response to the deactivation
of the first switch signal S1. Alternatively, when the temperature
T2 of the second cooling conductor 210 becomes equal to or lower
than a predetermined temperature (e.g. 90 K), the second
temperature sensor 220 deactivates the second switch signal S2.
Then, the first thermal conduction switch SW1 is turned OFF in
response to the deactivation of the second switch signal S2.
[0044] Alternatively, the first thermal conduction switch SW1 may
be formed of bimetal. For example, the bimetal is so formed as to
be in contact with the first cooling conductor 110. When the
temperature T1 of the first cooling conductor 110 becomes equal to
or lower than a predetermined temperature (e.g. 60 K), the bimetal
is detached from the second cooling conductor 210. Consequently,
the first thermal conduction switch SW1 is turned OFF.
Alternatively, the bimetal is so formed as to be in contact with
the second cooling conductor 210. When the temperature T2 of the
second cooling conductor 210 becomes equal to or lower than a
predetermined temperature (e.g. 90 K), the bimetal is detached from
the first cooling conductor 110. Consequently, the first thermal
conduction switch SW1 is turned OFF.
[Heating Stage]
[0045] FIG. 5 is a schematic view showing an operation at the time
of heating. At the time of the heating, the first cooling unit 100
and the second cooling unit 200 are turned OFF and the heater 300
is turned ON. Furthermore, according to the present embodiment, the
first thermal conduction switch SW1 is turned ON. Consequently, the
first cooling conductor 110 and the second cooling conductor 210
are connected with each other and thus the heat transfer between
the first cooling conductor 110 and the second cooling conductor
210 is possible. Owing to the heat intrusion through the current
lead 30 and heat generated by the heater 300, the temperatures of
the first cooling conductor 110, the second cooling conductor 210,
the internal superconductor 10 and the superconductor 20 are
increased.
[0046] The first thermal conduction switch SW1 may be turned ON
manually by an operator. Alternatively, the first thermal
conduction switch SW1 may be turned ON automatically.
1-3. Effect
[0047] According to the present embodiment, the first cooling unit
100 whose lowest reachable temperature is low but whose cooling
capacity is small and the second cooling unit 200 whose lowest
reachable temperature is high but whose cooling capacity is large
are used together during the initial cooling of the internal
superconductor 10. It is therefore possible to reduce the cooling
time of the internal superconductor 10 without increasing capacity
of the cooling unit or providing an additional cooling equipment.
That is to say, a time to the starting-up of the operation of the
internal superconductor 10 can be shortened without increasing
costs.
2. Second Embodiment
2-1. Configuration
[0048] FIG. 6 is a schematic view showing a configuration of the
superconductor cooling system 1 according to a second embodiment of
the present invention. A description overlapping with the foregoing
first embodiment will be omitted as appropriate.
[0049] According to the present embodiment, as shown in FIG. 6, a
second thermal conduction switch SW2 is further provided on the
second cooling conductor 210. More in detail, the second cooling
conductor 210 has a cooling unit connector 210A located on a side
of the second cooling unit 200, a current lead connector 210B
located on a side of the superconductor 20 of the current lead 30,
and the second thermal conduction switch SW2 connected between the
cooling unit connector 210A and the current lead connector 210B.
The second thermal conduction switch SW2 has the same configuration
as the first thermal conduction switch SW1 and turns ON/OFF heat
transfer between the cooling unit connector 210A and the current
lead connector 210B. The second thermal conduction switch SW2 may
have a configuration as shown in FIG. 2, or may be formed of
bimetal whose shape and displacement are changed depending on
temperature.
[0050] The first thermal conduction switch SW1 is connected between
the first cooling conductor 110 and the cooling unit connector 210A
of the second cooling conductor 210. The first thermal conduction
switch SW1 has the same configuration as in the first embodiment
and turns ON/OFF heat transfer between the first cooling conductor
110 and the cooling unit connector 210A.
[0051] The first temperature sensor 120 detects the temperature T1
of the first cooling conductor 110 and outputs the first switch
signal S1 depending on the detected temperature T1. The second
temperature sensor 220 detects the temperature T2 of the cooling
unit connector 210A of the second cooling conductor 210 and outputs
the second switch signal S2 depending on the detected temperature
T2.
2-2. Operation
[0052] [Initial cooling stage]
[0053] FIG. 7 is a schematic view showing an operation at the time
of, initial cooling. At the time of the initial cooling, the first
cooling unit 100 and the second cooling unit 200 are turned ON and
the heater 300 is turned OFF. Furthermore, according to the present
embodiment, the first thermal conduction switch SW1 is turned ON
and the second thermal conduction switch SW2 is turned OFF.
Consequently, the first cooling conductor 110 and the cooling unit
connector 210A are connected with each other and thus the heat
transfer between the first cooling conductor 110 and the cooling
unit connector 210A is possible. Moreover, the cooling unit
connector 210A and the current lead connector 210B are disconnected
from each other and thus the heat transfer between the cooling unit
connector 210A and the current lead connector 210B is
prevented.
[0054] As a result, the internal superconductor 10 is cooled (heat
removal) through both of the first cooling conductor 110 and the
cooling unit connector 210A. That is to say, not only the first
cooling unit 100 but also the second cooling unit 200, which is
originally used for cooling the superconductor 20, is used together
during the initial cooling of the internal superconductor 10. Since
the first cooling unit 100 and the second cooling unit 200 are used
together, a total cooling capacity is improved and thus the initial
cooling can be performed in a short time. Furthermore, since the
second thermal conduction switch SW2 is turned OFF, the second
cooling unit 200 and the current lead 30 are disconnected from each
other. In this case, the second cooling unit 200 is not affected by
heat intrusion through the current lead 30, and thus overall
cooling capacity of the second cooling unit 200 can be fully used
for cooling the internal superconductor 10. Therefore, the cooling
time of the internal superconductor 10 can be reduced further.
[0055] The first thermal conduction switch SW1 and the second
thermal conduction switch SW2 may be respectively turned ON and OFF
manually by an operator.
[0056] Alternatively, the first thermal conduction switch SW1 and
the second thermal conduction switch SW2 may be respectively turned
ON and OFF automatically. For example, when the temperature T1 of
the first cooling conductor 110 is higher than a predetermined
temperature (e.g. 60 K), the first temperature sensor 120 activates
the first switch signal S1. When the first switch signal S1 is
activated, the first thermal conduction switch SW1 is turned ON.
When the temperature T2 of the cooling unit connector 210A is
higher than a predetermined temperature (e.g. 90 K), the second
temperature sensor 220 deactivates the second switch signal S2.
When the second switch signal SW2 is deactivated, the second
thermal conduction switch SW2 is turned OFF. Alternatively, both of
the first thermal conduction switch SW1 and the second thermal
conduction switch SW2 may be controlled by the second switch signal
S2. In this case, the first thermal conduction switch SW1 is turned
ON and the second thermal conduction switch SW2 is turned OFF when
the second switch signal S2 is deactivated.
[0057] Alternatively, the first thermal conduction switch SW1 may
be formed of bimetal as described in the first embodiment.
Moreover, the second thermal conduction switch SW2 may also be
formed of bimetal as in the case of the first thermal conduction
switch SW1. In this case, the bimetal is so formed as to be in
contact with the cooling unit connector 210A. When the temperature
T2 of the cooling unit connector 210A is higher than a
predetermined temperature (e.g. 90 K), the bimetal is detached from
the current lead connector 210B. Consequently, the second thermal
conduction switch SW2 is turned OFF.
[Late Cooling Stage and Running Stage]
[0058] FIG. 8 is a schematic view showing an operation at the time
of late cooling and running. As shown in FIG. 8, the first thermal
conduction switch SW1 is turned OFF and the second thermal
conduction switch SW2 is turned ON. Consequently, the first cooling
conductor 110 and the cooling unit connector 210A are disconnected
from each other and thus the heat transfer between the first
cooling conductor 110 and the cooling unit connector 210A is
prevented. Moreover, the cooling unit connector 210A and the
current lead connector 210B are connected with each other and thus
the heat transfer between the cooling unit connector 210A and the
current lead connector 210B is possible. At this time, the internal
superconductor 10 is cooled (heat removal) by the first cooling
unit 100 through the first cooling conductor 110. Moreover, the
superconductor 20 is cooled (heat removal) by the second cooling
unit 200 through the second cooling conductor 210.
[0059] When the first cooling conductor 110 and the internal
superconductor 10 are cooled to near the first temperature (20 K)
and the second cooling conductor 210 and the superconductor 20 are
cooled to near the second temperature (60 K), the late cooling is
ended. After that, the current is supplied to the internal
superconductor 10 from the external power supply 60 through the
current lead 30. At the time of the power distribution to the
internal superconductor 10 (the running stage), the first thermal
conduction switch SW1 is maintained at the OFF state and the second
thermal conduction switch SW2 is maintained at the ON state. The
temperature of the internal superconductor 10 is maintained by the
first cooling unit 100 and the temperature of the superconductor 20
is maintained by the second cooling unit 200.
[0060] The first thermal conduction switch SW1 and the second
thermal conduction switch SW2 may be respectively turned OFF and ON
manually by an operator.
[0061] Alternatively, the first thermal conduction switch SW1 and
the second thermal conduction switch SW2 may be respectively turned
OFF and ON automatically. For example, when the temperature T1 of
the first cooling conductor 110 becomes equal to or lower than a
predetermined temperature (e.g. 60 K, which is the target
temperature of the superconductor 20), the first temperature sensor
120 deactivates the first switch signal S1. Then, the first thermal
conduction switch SW1 is turned OFF in response to the deactivation
of the first switch signal S1. Also, when the temperature T2 of the
cooling unit connector 210A becomes equal to or lower than a
predetermined temperature (e.g. 90 K), the second temperature
sensor 220 activates the second switch signal S2. Then, the second
thermal conduction switch SW2 is then ON in response to the
activation of the second switch signal S2. Alternatively, both the
first thermal conduction switch SW1 and the second thermal
conduction switch SW2 may be controlled by the second switch signal
S2. In this case, the first thermal conduction switch SW1 is turned
OFF and the second thermal conduction switch SW2 is turned ON in
response to the activation of the second switch signal S2.
[0062] Alternatively, the first thermal conduction switch SW1 may
be formed of bimetal as described in the first embodiment.
Moreover, the second thermal conduction switch SW2 may also be
formed of bimetal as in the case of the first thermal conduction
switch SW1. In this case, the bimetal is so formed as to be in
contact with the cooling unit connector 210A. When the temperature
T2 of the cooling unit connector 210A becomes equal to or lower
than a predetermined temperature (e.g. 90 K), the bimetal also
comes into contact with the current lead connector 210B.
Consequently, the second thermal conduction switch SW2 is turned
ON.
[Heating Stage]
[0063] FIG. 9 is a schematic view showing an operation at the time
of heating. At the time of the heating, the first cooling unit 100
and the second cooling unit 200 are turned OFF and the heater 300
is turned ON. Further, according to the present embodiment, the
first thermal conduction switch SW1 and the second thermal
conduction switch SW2 are turned ON. Consequently, the first
cooling conductor 110 and the cooling unit connector 210A are
connected with each other and thus the heat transfer between the
first cooling conductor 110 and the cooling unit connector 210A is
possible. Moreover, the cooling unit connector 210A and the current
lead connector 210B are connected with each other and thus the heat
transfer between the cooling unit connector 210A and the current
lead connector 210B is possible. Owing to the heat intrusion
through the current lead 30 and heat generated by the heater 300,
the temperatures of the first cooling conductor 110, the second
cooling conductor 210, the internal superconductor 10 and the
superconductor 20 are increased.
[0064] The first thermal conduction switch SW1 and the second
thermal conduction switch SW2 may be turned ON manually by an
operator. Alternatively, the first thermal conduction switch SW1
and the second thermal conduction switch SW2 may be turned ON
automatically.
2-3. Effect
[0065] According to the present embodiment, the same effects as in
the first embodiment can be obtained. Furthermore, during the
initial cooling, the second thermal conduction switch SW2 is turned
OFF and thus the second cooling unit 200 and the current lead 30
are disconnected from each other. As a result, the second cooling
unit 200 is not affected by heat intrusion through the current lead
30, and thus overall cooling capacity of the second cooling unit
200 can be fully used for cooling the internal superconductor 10.
Therefore, the cooling time of the internal superconductor 10 can
be reduced further. That is to say, the time to the starting-up of
the operation of the internal superconductor 10 can be shortened
further.
[0066] The present invention can be applied to a SMES
(Superconducting Magnetic Energy Storage), a superconducting cable,
a superconducting transformer, a superconducting generator, a
superconducting motor and so forth.
[0067] Embodiments of the present invention have been described
above by referring to the attached drawings. The present invention
is not limited to the above-described embodiments and changes may
appropriately be made by those who skilled in the art without
departing from the scope of the invention.
* * * * *